1. Field of the Invention
The present invention relates to a plasma processing apparatus and a plasma processing method which are employed in fabrication of semiconductor devices.
2. Description of the Related Art
Along with a recent tendency of semiconductor integrated circuits to high-density integration and high-processing speed performance, a gate electrode is requested to be further miniaturized. According to the International Technology Roadmap for Semiconductors 2008 Edition, a dimension of a gate of a 40 nm-node high-speed logic device has reached 22 nm in 2011, and precision in a processed dimension is requested to be equal to or smaller than 1.33 nm (3σ). In generations succeeding the 45 nm node, an existing silicon oxynitride (SiON)/polysilicon (poly-Si) gate electrode is being rapidly replaced with a high-dielectric constant (high-k) metal gate electrode in efforts to suppress a gate leakage current. However, since a minute variation in a dimension of a gate electrode leads to a large change in a source-drain current or a leakage current occurring on standby, stabilization of precision in the dimension (critical dimension (CD)) of the gate electrode or a processed shape thereof is a significant factor for improvement of a yield.
Conceivable as a factor for an adverse effect on the processed shape is the fact that a reaction by-product of etching may be deposited on the surface of a processing chamber. In this case, even when plasma is produced under the same condition, a quantity of consumed free radicals (hereinafter radicals) or a probability of recombination of radicals varies. The density of radicals in plasma is altered, and a processed shape is altered.
In order to improve a yield, occurrence of a pattern defect has to be suppressed. As one of causes of the pattern defect deriving from an etching processing apparatus, a deposit on the surface of the processing chamber is cited. A grown deposit peels off and drops onto a wafer at some time. Since the deposit that has dropped acts as a mask and hinders etching of an under-layer of the wafer. This brings about the pattern defect and invites a decrease in a product yield. The substance that hinders etching is called a foreign matter.
In order to improve the yield by achieving both a decrease in occurrence of a pattern defect and stabilization of a processed shape, proper dry cleaning of the surface of the processing chamber is necessary.
In the past, dry cleaning to be described below has been performed in order to remove a metallic deposit from the surface of the processing chamber. Japanese Patent Application Laid-Open Publication No. 11-140675 has revealed a method of cleaning out a titanium (Ti) deposit from the processing chamber by adding chlorine to a mixed gas of oxygen and methanol. Japanese Patent Application Laid-Open Publication No. 2006-237432 (Japanese Patent Application No. 2005-52434) has described that cleaning of an interior of the processing chamber is achieved by carrying out a process of removing a carbon-series substance using a mixed gas of oxygen and tetrafluorocarbon, and a process of removing a metallic film using a mixed gas of boron trichloride (BCl3) and dichloride (Cl2). Japanese Patent Application Laid-Open Publication No. 2001-176843 has unveiled a method of reducing a quantity of foreign matters by attaching a fluorocarbon film after completion of cleaning out an aluminum component using a mixed gas of BCl3 and Cl2.